Grate the zucchini and squeeze out all excess moisture using a clean kitchen towel to ensure the fritters stay crispy.
In a small bowl, whisk the egg and then stir in the zucchini, chickpea flour, and half of the sea salt, black pepper, and garlic powder.
Pat the mackerel fillets completely dry with a paper towel and season the flesh side with the remaining salt, pepper, and garlic powder.
Heat half of the olive oil in a non-stick skillet over medium-high heat and cook the zucchini mixture in small, flattened mounds for 3-4 minutes per side until golden.
Wipe the skillet, add the remaining oil, and sear the mackerel skin-side down for 3 minutes until the skin is shatteringly crisp, then flip and cook for 2 more minutes.
In a small ramekin, stir together the Greek yogurt and lemon juice to create a bright, zesty sauce.
Plate the crispy mackerel alongside the fritters and serve with the lemon-yogurt sauce on top.